Member postings for Robin Graham

This doesn't seem to be a problem for me, but I came across discussions of the influence of lathe tailstock height misalignment on turning parallel between centres whilst looking for other related info. The discussions were initiated by people who had bought a lathe and, by one method or another, had found the tailstock centre to be high with respect to the headstock. The advice from seasoned hands was not to worry - provided the tailstock is OK in the horizontal plane, vertical alignment (unless grossly out) would be insignificant, but no explanation was given. I wanted to understand this better and tried to work it out.

I'm very bad at 3-D visualisation so tried to approximate the problem by imagining that the tool was cutting dead on centre at the headstock and low by delta_h at the tailstock:

After a bit of algebra it came out that the radius at the tailstock end would be the radius at the headstock plus the square of the distance of the tool under centre at the tailstock divided by the diameter of the work at the headstock.

If this is so, it would explain to me why vertical alignment is relatively unimportant - on a nominal 10mm diameter workpiece, even if the tailstock were 0.1mm high it would lead to a discrepancy of 0.1x0.1/10 = 0.001mm on radius.

I'm not sure that I've set the problem up correctly though - I've a sneaky feeling that I've over simplified, and conic sections or something come into it. The intersection of a plane with a cylinder can be an ellipse, so maybe turning with the tailstock off-height gives a barrel shape - I just can't visualise it!

I realise that this may have little practical importance at home workshop levels of accuracy, but I'd like to understand it better.

Robin

Just to wind up with how it went. The repair didn't work (the spindle was too badly bent) so I reverted to plan A.

I set up to turn between centres:

and turned the outboard LH thread and other external features. I was pretty happy to find that (according to my Sunday Best Mtitutoyo mic) the parallel section was indeed parallel to 0.002mm over 100mm.

Because I had no easy way of doing the spring-loaded dog thing, I turned the work round, set it in the 4-jaw and centered on the bearing seats by fiddling with the chuck and the steady arms:

I then parted off the stub at the tailstock end (yes, I did take the tailstock off before finishing the cut), drilled, bored and reamed the internal taper and cut the RH thread with this setup.

The finished spindle:

has ~ 0.01mm TIR on the internal taper with respect the the bearing seats. OK, not great but not too bad.

I nearly had a heart attack when I spun up the (commercial) drive centre and saw the spur point wobbling visibly - but it turned out the commercial part was at fault. I guess it really doesn't matter so much with woodturning,

Many thanks for advice - I've learned a lot from this project, simple as it may seem to many of you.

Robin.

Edited By Robin Graham on 30/05/2021 00:13:13

Robin, I have a very similar lathe, albeit Axminster branded. It sits on the wonky flagstones of a 200 year old cellar, using eight (four per pillar) 80mm diameter rubber feet on M12 studs (I got them from WDS I think):

I was lucky enough to have to have the generous help of a professional engineer (the late John Stevenson) in setting the machine up. He spent half an hour muttering, twiddling the nuts and checking the ways with a level before announcing 'that's good enough'. No shimming or anything like that, and it was indeed 'good enough' - it turns parallel between centres to < 0.01mm over 400mm. The lathe weighs about 600kg, of which I reckon about 100-120 kg is in the stand and the rest in the machine - so it's the tail wagging the dog - but it seems to work.You'll get there! It won't twist after it's been set up properly - at least mine hasn't.

Your method of projecting the spindle axis by holding a piece of what looks like rolled BMS in a 3-jaw is, unfortunately, not good . For starters, the bar cannot be relied on to be round/straight and the chuck won't hold the bar dead on axis anyway. Then there's gravity. You need to think about what exactly you're measuring and why. And re-read what others have said upthread.

Another Robin.

I don't get out as much as I'd like these days (for obvious reasons) , but on a recent expedition I spotted this in the window of a new shop in my town:

I'm not sure where to start with the badness, but I'll have a go.

1. If they've gutted a working Wolf drill to make this monstrosity it is, if not a hanging offence, at least worth some sharp words from the bench.
2. If the drill was unrepairable (unlikely - they were were built to last) the stand would still be be useful - it looks well made.
3. Even as a piece of retro-industrial art it's a piece of dritt, as they might say in Norway. I don't want to use inappropriate English language and be censored.

The shop was closed when I passed so I couldn't ask what they wanted. I'll be down the town tomorrow and inquire, if it hasn't been snapped up.

Anyone want to guess the price , or give other examples?

Robin.

Edited By Robin Graham on 23/05/2021 23:59:57

Many thanks for taking the time to post those pics John - much appreciated. Often I am either confused by technical explanations (too hard) or frustrated by over simplifications (too soft), but the level of the text you reproduced is pure Goldilocks for me. Obviously I'm 100 years behind the times.

It turns out that the spindle in question was knackered by an over-enthusiastic attempt to remove the original bearings, and the damage is limited to the threaded portion to the left of the flange in my earlier pic. In which case I might be able to fix it without having to make a new spindle. Shucks, I was looking forward to the challenge. I might have to do it anyway, just because I think I can.

Robin.

Edited By Robin Graham on 16/05/2021 23:25:34

Thanks for further suggestions. I think I now have enough to be going on with with - I have plenty of 1" scrap to play with, so shall try various things in the hope that when I get to the job proper I'll have a rational 'schedule of operations' (I've learned some new vocab there!) worked out and get it right in one go.

NDIY - I am planning to buy a MT1 soft arbor if only to line up the topslide for initial boring (I don't have any MT1 tooling) , so good to hear that you have found they can be useful for between centres work.

John - many thanks for the illustration and accompanying text. That's very useful. Can you give a reference? I want to see Fig 28! And where does the universal grinding machine (I haven't got one) come into the story I wonder?

The manufacturer (Nu-Tool) of the lathe supplied a nut to fit on the threaded nose of the spindle - the idea being that unscrewing the nut will eject the centre. I don't understand why they also made the spindle hollow, but I could drill it through if there is good reason.

Hopper - you are right - for a woodworking lathe it's not worth chasing tenths. But maybe someday I'll want to make a precision spindle or a precision something else, and this experience will be useful. So I want to get it as good as I can. I take your point about the centre disappearing down the hole - I shall tread softly.

Robin.

Thanks for replies. Obviously many ways to skin this cat - sadly I won't be able to use John Pace's grinding technique because - well, I can't. Looks like a nice way if you've got the kit though! The idea of a making Morse taper boring bar is interesting - I could probably do that.

I've now bought the tools pictured in my opening post though (only one remaining, order within 39 minutes for next day delivery - I'm a sucker for that sort of sales pressure) so shall experiment with them bearing in mind advice about achieving concentricity.

I'm sure I can make the spindle to acceptable tolerances one way or another, but I'm going through a 'get it right first time man' phase. I'm bad at planning lathe machining sequences to avoid resetting the work, losing concentricity and having to resort to the 4-jaw though.

This is the spindle I want to reproduce:

The internal 1MT taper is on the left - the rest of the spindle is solid. My thinkings so far, based on the kit
I have are:

1. Mount an oversized bar between centres, turn the external features then remount on-axis in the 4-jaw to make the taper.
2. Make the taper first in oversized bar, put a small 60 degree chamfer at the end, mount between centres and then do the external features.
3. Make the taper in oversize bar first, bung in a 1MT soft arbor and rely on the centre hole in the soft end of the arbor to turn the external features between centres.
4. None of the above

It's for a wood turning lathe, so a couple of thou out isn't going to be a problem, but I want to get it as accurate as I possibly can - I took the job on for a small, but negative, financial gain as a way of advancing my skills and doing someone else a bit of good.

Robin.

Edited By Robin Graham on 14/05/2021 01:18:58

Edited By Robin Graham on 14/05/2021 01:27:37

Edited By Robin Graham on 14/05/2021 01:36:01

I've been asked to make a spindle with an internal MT1 taper. I'm pretty sure that I can do it, at last resort by trial and and error with a slender boring tool, but it's a challenge because MT1 is only ~ 9.4 mm at the thin end and about 54mm deep. It'd take a long time and much blue (Stuarts and language) I expect.

Looking for an alternative approach I came across these reamers:

The top one is 'roughing' and the other finishing. But I don't know how they are meant to be used. Could I get away with step drilling or boring, then use the rougher to take off the corners and finish with the other? They are cheap Oriental offerings made from carbon, not HS, steel, but it's a one-off in EN1A so maybe it could work.

Has anyone used these tools and can advise? Or any suggestions for other methods?

Robin.

Edited By Robin Graham on 12/05/2021 02:17:04

Edited By Robin Graham on 12/05/2021 02:22:13

Thank you Jason and Nigel for further info. Some more ideas to try - as I have several to do it is worth my time experimenting to get this technique under my belt. Apart from the pleasure of learning something new!

In my first (successful) attempt I went through until I saw a bit of a bulge emerging on the back of the work, then turned it over and took off the bulge with the trepanning tool. I then knocked out the centre piece and finished by boring. I can see that trying to go all the through without a centre support as Nigel suggests would be a surefire recipe for disaster.

Thanks again for all the suggestions , Robin.

Thanks for replies. I confess that I didn't think this through too well - I just ground a 4mm square bit with enough clearance on the outside edge. As I (sort of) got away with it the first time I thought, pending arrival of a more suitable piece of HSS, I'd try another disc and experiment with speeds and feeds. The tool broke.

I haven't got Mason's book, but Andrew's comment that the tool should be half the width and twice the height (ie 2mm wide by 8mm high) made me think - surely that would foul on the outside edge? So I calculated:

It seems that for my 100mm hole a 2mm thick by 14mm high tool in that geometry would (just!) clear if I've got it right. Obviously that might not be the optimal tool geometry, it was just to give me a starting point. If any kind soul has a pic of Mason's tool shape to share, that would be interesting.

Hopper - I had to read your point about the notch about six times, but I think the penny has now dropped. Possibly!

Robin.

Edited By Robin Graham on 09/05/2021 00:10:16

Edited By Robin Graham on 09/05/2021 00:11:46

I have a job which involves making 100mm holes in 150mm x 6mm discs of black plate:

As I have a few to do, and the cutouts would be more useful than a bucket of swarf, I thought I would have ago at making a trepanning tool.

As you can see, it worked - but there is room for improvement.

I made the tool from a piece of 4mm square HSS:

I locked top and cross slides and fed manually using the saddle handwheel. Spindle speed was 65rpm giving ~20 m/min cutting speed.

What I found was that sometimes the tool chattered with a low grumbling sound, sometimes it squealed, and sometimes it went like a hot knife through butter. The discs were bought off eBay so I don't know how consistent the metal is, but my gut feeling is that the variation in behaviour was more likely to do with my inability to maintain a steady feed - especially as I've never done this before, so was perhaps overly hesitant. Something I've learned about parting off is that hesitancy is not good!

If so, I suppose power feed might be the way - but I have no idea what feed would be appropriate.

Or maybe the tool geometry is wrong. I used 4mm square because I had it - but perhaps that's not rigid enough and I should be using rectangular section, more like parting tool geometry.

Sorry that this is a bit rambling and unfocused - any education about this technique would be most welcome.

Robin.

Thanks for suggestions.

I had tried clingfilm - I couldn't get it to stick reliably. It is also quite thin at ~ 10μm.

I've used Renaissance wax for metal finishing, and it's good stuff I agree - but not really what I want here. Corrosion isn't the problem, it's a need to protect the work from the scratch demons which seem to inhabit my workshop. Or to put it another way, to protect the work from my sloppy and inconsistent practices.

I have MetalGuard from ARC - it's great for what it's meant for, but it's not what's needed here.

I had thought about painting or spraying with some sort of protective film, but then it has to be removed with a solvent, which would give further scope to the scratch demons.

It sounds like the vinyl transfer tape which Adam suggested might work. I had a look (I wasn't aware of the technology) and have ordered a roll. I went for the brand which had the most negative reviews for the intended purpose - 'not sticky enough'. It won't need it to be in place for more than a few days,

Many thanks to Pete and Adam for offering samples - very much appreciated, but I succumbed to the lure of 'Free delivery: Tomorrow. Order within 14 minutes'. So the stuff should be with me tomorrow - or later today, looking at the clock now.

Robin

Edited By Robin Graham on 05/05/2021 00:13:55

Edited By Robin Graham on 05/05/2021 00:14:43

Edited By Robin Graham on 05/05/2021 00:35:32

Edited By Robin Graham on 05/05/2021 00:50:23

I've been spending some time polishing brass lately. I would like to be able to protect finished parts (flat surfaces, nothing complicated) pending assembly. I had a look for protective film - the sort of stuff that you peel from metal sheets supplied as polished - but found only industrial-quantity suppliers.

Does anyone know where I could get small quantities? Or are there any suggestions for DIY alternatives? Obviously it's important that the film leaves no discernible residue when peeled off.

Robin.

Chris, I doubt that you have created anything like Prussian Blue by sticking a chisel in a lump of lime wood. I think it's more likely that what you are seeing is the result of the reaction of iron with tannins in the wood - the complexes which form can be anywhere from blue to black.

For example, here is a pic of rust treated with 'tannic acid' -

Robin (who was once a chemist).

Hi Neils. My lathe is of the generic Chinese 12x36 design - there are many variations, but the particular variant I have came from Axminster Tools. You can find a manual which gives some info about the headstock / screwcutting gearbox internals here . In the US Grizzly used to sell a very similar machine, marketed as a gunsmith's lathe - the (rather more detailed) manual for their variant can be found here . The Grizzly headstock spindle and gearbox arrangements appear to be identical to those in my machine, but the threading / power feed box is somewhat different.

[Edit] I had a quick look and it seems the CJ0625 - if that's the one you're looking at- is an entirely different animal, so the above might not be of much use!

If I can help further it might be better to continue discussion by private message, as its a bit off-topic here.

Thanks for the link to the discussion of carbide parting tools on HMEM. Your step parting technique is interesting - as well as the Greenwood tool (which uses 2.2mm Sandvik Coromant inserts I think) I have an ARC tool which uses 3mm GTN inserts, so it could be a useful method for me in some circumstances.

Robin.

Edited By Robin Graham on 30/04/2021 23:11:42

Edited By Robin Graham on 30/04/2021 23:15:04

Edited By Robin Graham on 30/04/2021 23:18:17

Thanks all - just what I needed. I have bought inserts from JB (and had excellent service), but didn't think to look there. An order will be winging its way to JB.

Niels - thanks for the link to your ultra-rigid holder. That looks good. Apart from your holder, the thread is informative in general about the use of carbide tooling in a home workshop.

It's sad to hear that Greenwood is closing. I have a KIT-Q-CUT parting tool which I bought from them years ago at a show (remember shows?). It's a wonderful tool - zips its way though pretty much anything.

Robin.

I have quite a few CCMT/CCGT inserts which are worn or chipped on the 80 degree corners but pristine on the 100 degree. I can't find holders to use the 100 degree corners though - probably not using the right search terms. They must exist!

Can anyone advise?

Robin.

Thanks for replies - I think my questions have been answered. Neil Lickfold's detailed report on speeds, feed &c is especially useful.

It seems that I shall have to don my bio-hazard gear and crawl under the lathe to inspect the suds sump. I rarely use flood coolant (messy) but it sounds like I should for this task.

I don't intend to invest in a class D extinguisher, but might run to a tub of finely-powdered salt which might be better than sand in the event of an emergency. Apparently that's what's in the extinguishers - the salt melts and make a crust over the blazing inferno. And presumably sucks out some energy in the latent heat of fusion.

Something in the article Dave linked to confused me at first:

"Use of relatively high speeds of travel. Temperature is less influenced by speed of travel than by cutting speed. Travel speeds should therefore be as high as compatible with efficient working."

I initially read that as the statement of a general principle, which I couldn't understand. On reflection I think it's to do with the low thermal conductivity of titanium. Presumably the high rate of travel just distributes the heat over the work more rapidly than thermal diffusion, and therefore results in lower local temperatures. Is that right?

Mick - I had thought about carbide drills but was put off by the cost. Nearly £50 for a 5mm drill from RS! But Ive found that Zoro list a 5mm Dormer carbide stub drill, which will do me fine, for £5.99. I don't need to drill deeper than 8mm  so I'll probably go that way.

Robin.

Edited By Robin Graham on 27/04/2021 00:25:39

Edited By Robin Graham on 27/04/2021 00:26:11

This is not the first thread on this forum with the title above I know - I found a discussion dating from 2011 (it ran for four years in fits and starts!) but it doesn't give me the info I want. I think the OP in that thread wasn't specific enough in his question, so I'll try to focus:

I have a piece of 20mm diameter Grade 5 (Ti 6-4) round bar which I want to cut, turn, and drill.

• Q1. Can this stuff be cut with a 'normal' bandsaw? Mine has a 14tpi bimetal blade with M42 teeth. The blade speed given on the plate is 45/min, but it doesn't say if the 45 is in nanometres, parsecs or somewhere between.
• Q2. If I use carbide insert tools for the turning, should I go for CCMT or CCGT? Or would I be better off with HSS?
• Q3. I've looked about for advice on drilling the stuff and the recommendation is solid carbide. But that's from suppliers of industrial tooling. I need to drill three holes. Can I get away with HSS drills?

Any advice would be welcome.

Robin.

But aren't the shanks of HSS drills much softer than the business end? I've certainly scored drill shanks when I've not tightened the drill chuck enough. And is bronze really hard/strong enough for this sort of thing? The numbers (hardness / Young's modulus) suggest not. But it's never that simple I suppose. Or maybe the smiley means it's a joke. I don't know - I'm a tyro, you could probably send me to the store for a metric monkey wrench.

I did get eventually get a half-decent knurl with my improvised tool:

but it's not sharp.

I think I have to make a clamp-type tool. David George has kindly sent me detailed plans for his version - thank you David.

Robin.